1. Field of the Invention
The present invention relates to phase change inks and encompasses new colorless compounds which can be utilized as toughening agents in phase change inks. The invention also encompasses solid phase change inks having the colorless compounds incorporated therein, and printing methods utilizing the phase change inks.
2. Description of the Related Art
The present invention encompasses new toughening compounds, routes to their preparation, and methodology for incorporating such compounds into phase change inks. Phase change inks are compositions which are in a solid phase at ambient temperature, but which exist in a liquid phase in an elevated operating temperature of an ink jet printing device. At the jet operating temperature, droplets of liquid ink are ejected from the printing device. When the ink droplets contact the surface of a printing media, they solidify to form a printed pattern. Phase change ink methodology is described generally in U.S. Pat. Nos. 4,889,560; 5,372,852; 5,827,918 and 5,919,839.
A difficulty associated with phase change inks can occur in automated document feed applications. Specifically, a substrate (such as, for example, paper) coated with a phase change ink can be difficult to utilize in automated document feed applications. The difficulty can occur if a coefficient of friction of the printed phase change ink is high enough to impede flow of the printed document through automated document feed systems, and can lead to document mis-feeding.
Additional difficulties that can occur with printed phase change inks result from the inks occasionally being too brittle, and accordingly lacking durability. If the inks are too brittle and are printed as an image on a flexible substrate, the printed inks can break when the substrate is bent. Such breakage can reduce a quality of the printed image.
It is often difficult to find a suitable ink composition which will have both appropriate durability and coefficient of friction. Frequently, modifications which improve ink suitability in automated document feed mechanisms (i.e., which reduce ink coefficient of friction) also decrease ink durability.
A general class of compounds developed for reducing some or all of the above-described difficulties are so-called toughening agents. Toughening agents are materials which can be incorporated into a phase change ink (i.e., utilized as an additive to the ink), and which improve durability of the printed ink to bending. The most ideal toughening agents not only improve the durability of the ink to bending, but do so without increasing a coefficient of friction of the ink relative to the coefficient of friction which would exist without the toughening agent.
It would be desirable to develop additional toughening agents which could be utilized in phase change inks for improving durability of the inks, and which preferably would not increase coefficient of frictions associated with the inks.
In one aspect, the invention encompasses a colorless compound comprising a central core and at least two arms extending from the core. The core can comprise one or more atoms. The at least two arms have the formula 
In such formula, Z is a segment of one or more atoms; j is an integer from 1 to about 300 and can be different at one of the at least two arms than at another of the at least two arms; Q is an alkyl or aryl group and can vary amongst different alkyl and aryl groups within the colorless compound; and n is an integer greater than 1 and can be different at one of the at least two arms than at another of the at least two arms. In other aspects, the invention encompasses phase change inks incorporating the above-described colorless compound as a toughening agent, and methods of printing with such phase change inks.
In another aspect, the invention encompasses a solid ink comprising a colorant and a colorless compound of the formula 
In such formula, X is a single atom corresponding to N or 0; Z1 and Z2 are substituents comprising one or more atoms, and can be the same as one another or different from one another; j is an integer from 1 to about 50; and the representation of xe2x80x9c(H, Q)xe2x80x9d indicates that either a group Q or a hydrogen can be in the shown positions. The group Q is either an alkyl group or an aryl group, and can vary amongst different alkyl and aryl groups within the compound.